ci: verify checkpoint portability on Windows

.github/workflows/ci.yml

@@ -393,6 +393,61 @@ jobs:
           if-no-files-found: error
           retention-days: 90
 
+  checkpoint-windows:
+    name: Checkpoint contracts (Windows)
+    runs-on: windows-latest
+    timeout-minutes: 15
+    env:
+      CUDA_VISIBLE_DEVICES: ""
+      HF_DATASETS_OFFLINE: "1"
+      HF_HUB_DISABLE_TELEMETRY: "1"
+      HF_HUB_OFFLINE: "1"
+      TOKENIZERS_PARALLELISM: "false"
+      TRANSFORMERS_OFFLINE: "1"
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+
+      - name: Set up Python
+        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
+        with:
+          python-version: "3.12"
+          cache: pip
+          cache-dependency-path: |
+            pyproject.toml
+            uv.lock
+
+      - name: Install locked test environment
+        shell: pwsh
+        run: |
+          python -m pip install "uv==$env:UV_VERSION"
+          $testEnv = Join-Path $env:RUNNER_TEMP "obliteratus-checkpoint-windows"
+          $env:UV_PROJECT_ENVIRONMENT = $testEnv
+          uv sync --locked --no-default-groups --extra dev --no-editable
+          "CHECKPOINT_TEST_ENV=$testEnv" >> $env:GITHUB_ENV
+
+      - name: Run Windows checkpoint contracts
+        shell: pwsh
+        run: |
+          $python = Join-Path $env:CHECKPOINT_TEST_ENV "Scripts/python.exe"
+          & $python -m pytest `
+            tests/test_checkpoint_atomicity.py `
+            tests/test_persistence_contracts.py `
+            tests/test_persistence_pipeline.py `
+            --no-cov `
+            --junitxml="$env:RUNNER_TEMP/checkpoint-windows.xml" `
+            -q
+
+      - name: Upload Windows checkpoint evidence
+        if: always()
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: checkpoint-evidence-windows-py3.12
+          path: ${{ runner.temp }}/checkpoint-windows.xml
+          if-no-files-found: error
+          retention-days: 90
+
   quality-depth:
     name: Quality depth
     runs-on: ubuntu-latest